Benzo-pyrene-transformed 3T3 (BP-3T3) cells can be arrested in the G1-phase of their cell cycle by a 100-fold reduction in the serum concentration of the growth medium. Under such conditions alpha-aminoiso-butyric acid uptake is reduced 3-fold. However, the uptake of uridine and certain glucose analogs is not reduced. This is in contrast to "normal" 3T3 cells which exhibit decreased transport rates for these same compounds. This suggests that hexose sugar and uridine uptake changes occurring during G1-arrest of 3T3 cells may be G0-specific events, or that the Gl-arrest states in normal and trnsformed cells have different characteristics. The H6-15 subline of SV-3T3 cells is a temperature-sensitive derivative which demonstrates normal growth behavior at 39 degrees C, but transformed behavior at 32 degrees C. 3-0-methylglucose transport is 2-4-fold higher when the cells are grown at 32 degrees C. However, at both the restrictive and permissive temperatures there is a marked cell density-dependent reduction in uptake. This seems inconsistent with hexose sugar transport activity being a determinant of growth potential of transformed cells. In addition, preliminary experiments indicate a 3-4-fold difference in serum component-depletion activity when cells are grown at 32 degrees C. This is consistent with the hypothesis that transformed cells have reduced serum requirements for growth.